McCain: Travelers to N Korea should sign waiver

Moon's spokesman Park Soo-hyun told the media that the President expressed regrets for the United States university student's death in the letter sent to the Warmbier family.

Roughly three years before he was taken prisoner in North Korea, Otto Warmbier spoke to his graduating high school class about persevering through "the good times and the bad", and holding onto friendships "to make things better".

The United States should consider an executive order immediately banning all tourist travel to North Korea for the time being, a major USA think tank said Wednesday amid outrage over the death of an American student following his comatose release from the North.

The travel agency specialises in North Korea tours and is based in the central Chinese city of Xi'an.

Last week, Tillerson told a Senate hearing that China's efforts on North Korea had been "uneven". The U.S. has been pressing Pyongyang to halt its nuclear weapons development and urging China and other countries to starve the North of funding for the program.

Warmbier was among the estimated 5,000 non-Chinese who visit North Korea every year on packages that often include trips to Pyongyang, the capital, as well as the demilitarized zone separating the two Koreas, Mount Paektu and sometimes the Masik ski resort.

The circumstances of his detention in North Korea and what medical treatment he may have received there remained a mystery, but relatives have said his condition suggested that he had been physically abused by his captors.